Hello,
I have a 230te and had a similar problem after doing the head gasket but it cured itself so I put it down to air in the system ref above post.
Spoke to the dealer and he said the duo valves often go ,it is in front of the brake master cylinder ,has two pipes going into it and costs about £80!!You need the chassis no as there are loads of different types.
Hope this helps .
Hamish